Fix bug affecting latest Sandbox image, update notebook code

[robbibt]

Proposed changes

This PR fixes several bugs in DEA Notebooks that cause tests to fail on the latest experimental version of the DEA Sandbox image. This includes bug fixes for:

• How_to_guides/Detecting_seasonality.ipynb
• Real_world_examples/Intertidal_elevation.ipynb
• Tools/dea_tools/wetlands.py

And some re-writing of the Intertidal notebook to address the existence of the new DEA Intertidal product, including:

• Deprecating the old/bespoke contours_to_arrays function in favour of a more generically useful extract_vertices function for extracting the point vertices of any geometry

[review-notebook-app[bot]]

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[robbibt]

Hey @emmaai @Ariana-B, can I get a ✔️ on this PR to fix the test fails in the latest unstable Sandbox image?